Casing for a power supply



FIG. 1 is a perspective view of a casing for a power supply showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left view thereof;

FIG. 5 is a right view thereof;

FIG. 6 is top view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a casing for a power supply, as shown. 